Thermal interface materials

Abstract

A thermally conductive interface material includes a material and a thermally conductive and electrically insulating particulate filler dispersed in the material, wherein the particulate filler includes a first filler component and a second filler component, wherein the first filler component has a first thermal conductivity and an aspect ratio of between 0.5 - 1.5, and the second filler component has an aspect ratio of between 0.5 - 1.5 and a second thermal conductivity that is at least 50% greater than the first thermal conductivity, wherein between 40-70 vol.% of the total particulate filler includes a coarse constituent having a first mean particle size (d50) of between 20 and 120 µm, and between 10-25 vol.% of the total particulate filler includes a fine constituent having a mean particle size of between 100 nm and 5 µm, the fine constituent including at least 20 vol.% of the second filler component.

Description

THERMAL INTERFACE MATERIALSBACKGROUND

[0001] Thermally conductive interface materials are widely employed for the purpose of dissipating heat from heat-generating components such as semiconductor elements, power transistors, integrated circuits, and battery elements. Thermally conductive greases, gels, pastes, and sheets have been used as interfaces between the heat-generating components and heat-dissipating elements such as plates and fins. Numerous designs and materials for such thermal interfaces have been implemented, with the highest performance being achieved when gaps between the thermal interface and the respective heat transfer surfaces are substantially avoided to promote conductive heat transfer from the electronic component to the heat dissipater. The thermal interface materials therefore preferably establish and maintain a robust interface between the somewhat uneven heat transfer surfaces of the respective components. Therefore, important physical characteristics of high-performance thermal interface materials are flexibility, dispensability, and low hardness.

[0002] In the case of dispensable materials, it is additionally important that the thermal interface is capable of wetting the heat transfer surface, and that the material provides suitable adhesive and cohesive strength to avoid delamination and to maintain the form and function of the interface over the anticipated working lifetime. Dispensable thermal interface materials therefore may be designed with a yield stress to avoid significant spreading after dispensing, or without a yield stress to maximally flow and penetrate surfaces. Curing behavior of the material may also be tailored to both avoid particle settling and to provide sufficient pre-cure time for re-work and handling.

[0003] Thermal conductivity is an important property of thermally conductive interface materials used for applications such as semiconductor elements, power transistors, integrated circuits, and battery elements. To promote increased thermal conductivity values, particulate fillers have been added to a material, such as a non-reactive liquid, a reactive liquid, or a semicrystalline carrier. While these particulate fillers can increase thermal conductivity, fillers with particularly high thermal conductivity are very expensive and can adversely affect flowability / dispensability, electrical insulation, and / or mechanical characteristics. Electrically insulated interface materials are especially important in automotive and industrial applications. Accordingly, embodiments of the present disclosure provide thermally conductive andelectrically insulating interface materials with excellent dispensability and mechanical characteristics.SUMMARY

[0004] In some aspects, a thermally conductive interface material includes a material and a thermally conductive and electrically insulating particulate filler dispersed in the material, wherein the particulate filler includes a first filler component and a second filler component, wherein the first filler component has a first thermal conductivity and an aspect ratio of between 0.5 - 1.5, and the second filler component has an aspect ratio of between 0.5 - 1.5 and a second thermal conductivity that is at least 50% greater than the first thermal conductivity, wherein between 40-70 vol.% of the total particulate filler includes a coarse constituent having a first mean particle size (dso) of between 20 and 120 pm, and between 10-25 vol.% of the total particulate filler includes a fine constituent having a mean particle size of between 100 nm and 5 pm, the fine constituent including at least 20 vol.% of the second filler component.

[0005] In some aspects, a thermally conductive interface material includes a polymer matrix and a thermally conductive and electrically insulating particulate filler dispersed in the polymer matrix, wherein the particulate filler includes a first filler component and a second filler component, wherein the first filler component includes alumina, and the second filler component includes aluminum nitride, wherein between 40-70 vol.% of the total particulate filler includes a coarse constituent having a first mean particle size (dso) of between 20 and 120 pm, and between 10-25 vol.% of the total particulate filler includes a fine constituent having a mean particle size of between 100 nm and 5 pm, the fine constituent including at least 20 vol.% of the second filler component.

[0006] In some aspects, an apparatus include: a heat producing component a heat dissipating component, and a thermally conductive interface material including: a material; and a thermally conductive and electrically insulating particulate filler dispersed in the material, wherein the particulate filler includes a first filler component and a second filler component, wherein the first filler component has a first thermal conductivity and an aspect ratio of between 0.5 - 1.5, and the second filler component has an aspect ratio of between 0.5 - 1.5 and a second thermal conductivity that is at least 50% greater than the first thermal conductivity, wherein between 40-70 vol.% of the total particulate filler includes a coarse constituent having a first mean particle size (dso) of between 20 and 120 pm, and between 10-25 vol.% of the totalparticulate filler includes a fine constituent having a mean particle size of between 100 nm and 5 pm, the fine constituent including at least 20 vol.% of the second filler component.BRIEF DESCRIPTION OF DRAWINGS

[0007] This written disclosure describes illustrative embodiments that are non-limiting and non-exhaustive. Reference is made to illustrative embodiments that are depicted in the figures, in which:

[0008] FIG. 1 illustrates apparatus 100 including thermally conductive interface material 130, according to some embodiments.

[0009] FIG. 2 illustrates the thermal conductivity of a thermal interface material as a function of the aluminum nitride volume fraction in the fine constituent, according to some embodiments.DETAILED DESCRIPTION

[0010] The objects and advantages enumerated above together with other objects, features, and advances represented by the present invention will now be presented in terms of detailed embodiments described with reference to the attached drawing figures which are intended to be representative of various possible configurations of the invention. Other embodiments and aspects of the invention are recognized as being within the grasp of those having ordinary skill in the art.

[0011] Embodiments of the present disclosure provide novel thermal interface material compositions. Often, thermal interface materials transfer heat from a heat generating component to a heat dissipating component. These thermal interface materials can be used for applications such as semiconductor elements, power transistors, integrated circuits, and battery elements. While conventional thermal interface materials have been used for transferring heat between various materials, these conventional thermal interface materials suffer from one or more of poor thermal conductivity, poor electrical insulation, inadequate dispensability, and utilization of expensive particulate fillers. The compositions of the present disclosure reduce the amount of high cost, high thermal conductivity particulate filler in the thermal interface material while maintaining excellent thermal conductivity and electrical insulation (resisting the flow of electric current).

[0012] Thermal interface materials of the present disclosure can include a material and a thermally conductive particulate filler. In one example, the material includes at least one of a non-curable polymer, oligomer, oil, and grease. In another example, the material includes a matrix material that can be chemically crosslinked. For example, the matrix material can include a polymer matrix (such as including an organopolysiloxane). The matrix material can be formed from at least a curable component(s) and a chemical cure activator. Preferably, a cure reaction is initiated with exposure between the curable component(s) and the cure activator, in some cases when in the presence of an environmental cure reaction facilitator, such as water, heat, pressure, electromagnetic radiation, and the like. For the purposes hereof, the presence of an environmental cure reaction facilitator is assumed if necessary to the cure reaction initiated with exposure between the curable component(s) and the cure activator. The cure activator therefore promotes a cure reaction involving the curable component(s).

[0013] In some embodiments, the curable component(s) may include a monomer, oligomer, or a polymer that is capable of undergoing a cross-linking reaction to form a network. The curable component(s) may include a catalyst. The chemical cure activator is preferably an agent that is initially separated from the curable component(s) to avoid a cure reaction, and subsequently introduced to the curable component(s) when the cure reaction is desired. In some embodiments, the cure activator includes a cross-linking agent. The cure activator may also or instead include a monomer, an oligomer, a polymer, a reaction initiator, a catalyst, and combinations thereof. The curable component(s) may include a first resin, and the cure activator may include a second resin that is reactive with the first resin. In some embodiments, the matrix may comprise an organic matrix including at least one of a thermoplastic resin and / or a thermoset resin.

[0014] The curable system of the curable component and the chemical cure activator may be selected from a wide variety of monomers, oligomers, and resins, wherein the term “resin” may include any natural or synthetic organic compound or mixture that is convertible into a polymer. An example cure reaction suitable for the curable systems of the present invention is the hydrosilylation from vinyl and hydride functional silicone resins. An example silicone may be an organosiloxane having the structural formula:wherein “x” represents an integer ranging from between 1 and 1,000. The thermally conductive interface material may be prepared as a reaction product of the organosiloxane together with a chain extender / cross-linker such as a hydride functional polydimethylsiloxane having the structural formula:wherein “x” and “y” each represent an integer having a value of between 1 and 1,000.

[0015] An example curable component of the present invention includes polydiorganosiloxanes, such as various vinyl or siloxy-terminated polydimethylsiloxanes (PDMS). Example commercially-available PDMS materials include Nusil PLY-7500 and 7905 available from Avantor, Inc.; Evonik VS 100, 200, 500, 10000, 20000, and 65000 available from Evonik Industries AG; and Gelest DMS-V21, V22, V41, V42, and V43 available from Gelest, Inc. The curable component may include one or more polymers that differ in, for example, molecular weight, viscosity, and molecular structure. For example, vinyl-terminated PDMS with viscosity values ranging from about 50 cP to about 1000 cP may be utilized.

[0016] The chemical cure activator may itself be reactive with the curable component and may include a cross-linker for a hydrosilylation reaction. The chemical cure activator may include a dihydroxy aliphatic chain extender such as a hydride-terminated polydimethylsiloxane. In one non-limiting example, if a chain extender is utilized, network modifiers such as mono-hydride terminated PDMS or mono-vinyl terminated PDMS may be utilized to tune the viscoelasticity and damping behavior of the PDMS. The silicon-bonded hydrogen atoms may be located at terminal, pendant, or at both terminal and pendant positions. The chemical cure activator may include one or more organohydrogenpolysiloxanes that may differ in at least one of molecular weight, viscosity, and molecular structure. Example commercially-available methylhydropolydimethylsiloxanes useful as a chemical cure activator that is reactive with the first reactant composition include Nusil XL-112 and XL-7505 available from Avantor, Inc.; Gelest HMS-071, 082, and 991 available from Gelest, Inc.; and Andisil XL-1B and 1340 available from AB Specialty Silicones. Hydride functional PDMS crosslinkers may be utilized, such as about 100 cP hydride functional PDMS crosslinkers. Ifthe curable component and the cure activator both include a catalyst, a silicone oil may be used to adjust the viscosity.

[0017] A variety of silane or silanol terminated resins may be employed in the matrices of the present invention. Condensation-curable silane- or silanol-terminated resins participate in a hydrolysis-condensation cure pathway, preferably at and above ambient temperatures. In some embodiments, the resins are non-silicone, wherein no more than a trace amount of silicone is contained in the composition. In some embodiments, no silicone is contained in the composition. Example resins suitable for the curable component of the present invention include reactive polymer resins with at least one silyl-reactive functional group, including at least one bond that may be activated with water. Example silyl -reactive functional groups include alkoxy silane, acetoxy silane, and ketoxime silane.

[0018] Other examples of curing reactions contemplated for the curable component and cure activator include a urethane reaction from hydroxyl and isocyanate functional monomers, oligomers, or resins, epoxy polymerization from epoxide and at least one of amino, mercapto, and anhydride functional monomers, oligomers, or resins, and radical polymerization of vinyl or vinylidene functional monomers, oligomers, or resins. In some embodiments, one or more of the monomers, oligomers, or resins may be in liquid form at 20 °C and 1 bar pressure and exhibit a viscosity of less than 1000 cP at 20 °C at a shear rate of 1 s'1. In some embodiments, one or more of the monomers, oligomers, or resins may be in liquid form at 20 °C and 1 bar pressure and exhibit a viscosity of less than 200 cP at 20 °C at a shear rate of 1 s'1. In one nonlimiting example, the reaction may be initiated from a two-part system, wherein Part A includes vinyl-terminated PDMS and a catalyst, and Part B includes vinyl-terminated PDMS and a hydride-functional crosslinker.

[0019] In some embodiments, the cure activator may include a catalyst, such as a reaction catalyst. A reaction catalyst may, for example, be employed to further facilitate the hydrosilylation reactions described above. Example reaction catalysts useful in the compositions of the present invention include platinum compounds, and organotin and organo- zinc and organo-titanium compounds (together referred to herein as “organo-metal catalyst”) that facilitate moisture cure of the silyl-modified reactive resins. In one example, the catalyst includes a Karstedt catalyst. For example, the Karstedt catalyst includes an organoplatinum compound derived from divinyl-containing disiloxane. Reaction catalysts used in the compositions of the present invention may be present in the range of 0 up to 0.5 percent byweight. In some embodiments, the compositions comprise in the range of 0.01 up to 0.5 percent by weight reaction catalyst.

[0020] The curable component of the present may be curable in the presence of water (moisture curable) at ambient temperature. Depending upon the application, the moisture may be available from the ambient environment or from water released from the object(s) to which the composition is applied. In some embodiments, the compositions of the invention are curable without addition of environmental moisture. In some embodiments, water may be included as an ingredient in a non-resin part of the multiple part curable composition, for mixture with the reactive constituents in situ. Preferably, however, the amount of water required in the composition itself is minor so as not to interfere with functional properties of the thermal material. In some embodiments, water is present in the compositions of the invention in the range of 0 up to 0.5 wt%. In some embodiments, the compositions comprise in the range of 0.01 up to 0.3 wt% water. In some embodiments, the compositions comprise in the range of 0.01 up to 0.2 wt% water.

[0021] The thermally conductive particulate filler (hereafter may be referred to as “particulate filler”) can be dispersed in the materials of the present disclosure. In one example, the particulate filler is dispersed in the polymer matrix. In another example, the particulate filler is dispersed / mixed with one or more components used for a cure reaction. The particulate filler generally includes thermally conductive and electrically insulating particulate fillers. In one example, the particulate filler includes at least one of alumina, aluminum trihydrate, zinc oxide, aluminum nitride, diamond, silicon carbide, silicon nitride, silicon dioxide, titanium dioxide, zirconia, magnesium oxide, and boron nitride. In another example, the particulate filler includes two or more of alumina, aluminum trihydrate, zinc oxide, aluminum nitride, diamond, silicon carbide, magnesium oxide, and boron nitride. In yet another example, the particulate filler includes alumina and aluminum nitride.

[0022] The particulate filler includes a first filler component and a second filler component. In one example, the first filler component includes one or more fillers of the present disclosure. In another example, the first filler component includes one or more of alumina (such as calcined alumina), aluminum trihydrate, magnesium oxide, aluminum nitride, and zinc oxide. The surface of the alumina may be unmodified. At least a portion of the alumina may exhibit an alpha or gamma crystal structure, or a mixture thereof. The first filler component has a first thermal conductivity, such as a first average thermal conductivity. The first thermalconductivity is generally at least about 5 W / m*K. In one example, the first thermal conductivity is at least about 10 W / m*K. In another example, the first thermal conductivity is at least about 20 W / m*K. The first filler component may have an aspect ratio ranging from about 0.5 to about 1.5. The aspect ratio may be defined as the ratio of the length to the width of the individual particle. In one example, the first filler component includes substantially spherical particles. In another example, the first filler component has an aspect ratio ranging from about 0.8 to about 1.2.

[0023] The second filler component includes one or more fillers of the present disclosure. In one example, the second filler component includes one or more of aluminum nitride and boron nitride, diamond, and silicon carbide. In another example, the second filler component includes aluminum nitride. The second filler component has a second thermal conductivity, such as a second average thermal conductivity. Importantly, the second thermal conductivity value is generally at least 50% greater than the first thermal conductivity value. In one example, the second thermal conductivity is at least 100% greater than the first thermal conductivity. The second thermal conductivity is generally at least about 50 W / m*K. In one example, the second thermal conductivity is at least about 100 W / m*K. In another example, the second thermal conductivity is at least about 120 W / m*K. The second filler component may have an aspect ratio ranging from about 0.5 to about 1.5. In one example, the second filler component includes substantially spherical particles. In another example, the second filler component has an aspect ratio ranging from about 0.8 to about 1.2.

[0024] The particulate filler includes a coarse constituent. The coarse constituent may provide the primary mechanism for heat transfer. In one example, about 40 vol% to about 80 vol% of the total particulate filler includes the coarse constituent. In another example, about 40 vol% to about 70 vol% of the total particulate filler includes the coarse constituent. In another example, about 50 vol% to about 70 vol% of the total particulate filler includes the coarse constituent. The coarse constituent generally has a first mean particle size (dso) of between 20 pm and 120 pm. In one example, the coarse constituent has a first mean particle size (dso) of between about 30 pm and about 120 pm. In another example, the coarse constituent consists of the first filler component. In yet another example, the volume ratio of the first filler component to the second filler component in the coarse constituent may range from 90: 10 to 40:60. In yet another example, the volume ratio of the first filler component to the second filler component in the coarse constituent ranges from 70:30 to 40:60.

[0025] The particulate filler includes a fine constituent. The fine constituent can provide thermal heat transfer sites / thermal bridges between larger filler particles (such as the coarse constituent). This can form an efficient pathway for thermal heat transfer. Generally, particles in the fine constituent are in contact with particles in the coarse constituent to enhance thermal heat transfer. In one example, about 10 vol% to about 60 vol% of the total particulate filler includes the fine constituent. In another example, about 10 vol% to about 40 vol% of the total particulate filler includes the fine constituent. In yet another example, about 10 vol% to about 25 vol% of the total particulate filler includes the fine constituent. The fine constituent generally has a second mean particle size (dso) of between 100 nm and 10 pm. In one example, the fine constituent has a second mean particle size (dso) of between about 100 nm and about 5 pm. In another example, the fine constituent has a second mean particle size (dso) of between about 1 pm and about 5 pm. The second mean particle size may be at least 10 times smaller than the first mean particle size.

[0026] Generally, the fine constituent includes at least 20 vol% of the second filler component. For example, the fine constituent includes about 20 vol% to about 100 vol% of the second filler component. In one example, the fine constituent includes about 40 vol% to about 60 vol% of the second filler component. As stated, the second filler component can include one or more of aluminum nitride and boron nitride. In another example, the fine constituent includes at least 40 vol% of the first filler component. In one example, the volume ratio of the second filler component to the first filler component in the fine constituent ranges from 10:90 to 80:20. In another example, the volume ratio of the second filler component to the first filler component in the fine constituent ranges from 20:80 to 70:30. In yet another example, the volume ratio of the second filler component to the first filler component in the fine constituent ranges from 40:60 to 60:40. Ratios of the second filler component in the fine constituent are important for overall thermal conductivity values, maintaining reasonable cost, and / or reducing total solids for mechanical requirements.

[0027] The particulate filler may include a medium constituent. The medium constituent may be used to enhance overall flowability of the thermal interface material. In one example, between about 1 vol% and about 30 vol% of the total particulate filler includes the medium constituent. In another example, between about 5 vol% and about 30 vol% of the total particulate filler includes the medium constituent. In another example, at least 10 vol% of the total particulate filler includes the medium constituent. The volume percentage of mediumconstituent in the total particulate filler is important to avoid disrupting the thermally conductive path. The medium constituent may include one or more of the first filler component, the second filler component, and a third filler component. The third filler component may include surface treated alumina. For example, the third filler component may include alumina with alkylsilane surface treatment. In one non-limiting example, the medium constituent consists of the third filler component. The medium constituent generally has a third mean particle size (dso) between about 5 pm and 20 pm. In one example, the third mean particle size (dso) ranges from about 7 pm to 12 pm. For example, the third mean particle size (dso) may be about 10 pm.

[0028] The particulate filler may include an ultrafine constituent. The ultrafine constituent may include one or more of the first filler component, the second filler component, and the third filler component. In one non-limiting example, the ultrafine constituent consists of the first filler component. In one example, the ultrafine constituent has a fourth mean particle size less than the second mean particle size. In another example, the ultrafine constituent may have a fourth mean particle size (dso) of less than about 1 pm. In another example, the ultrafine constituent may have a fourth mean particle size (dso) of less than about 100 nm.

[0029] The total volume percentage of all particulate filler in the thermal interface material may range from about 70 vol% to about 90 vol%. In one example, the total volume percentage of all particulate filler in the thermal interface material may range from about 75 vol% to about 85 vol%. In another example, the total volume percentage of all particulate filler in the thermal interface material may be greater than about 75 vol%.

[0030] In one example, the overall thermal conductivity of the thermal interface material is greater than about 5 W / m*K. In another example, the overall thermal conductivity of the thermal interface material is greater than about 5.5 W / m*K. In yet another example, the overall thermal conductivity of the thermal interface material is greater than about 6 W / m*K. In one non-limiting example, the overall thermal conductivity of the thermal interface material ranges from about 5 W / m*K to about 7 W / m*K. The dispense rate of the thermal interface material may be greater than 200 g / min. For example, the dispense rate of the thermal interface material may be greater than 250 g / min. In one non-limiting example for the dispense rate, one method is using a pressure-driven dispensing system with a 0.1” exit diameter, such as a Nordson EFD without a tip. In one example, a dispense rate over 100 g / min is desired. In one example, the electrical resistivity of the thermal interface material is at least 10!° Q*m. In another example,the electrical resistivity of the thermal interface material is at least 1011Q*m. In yet another example, the electrical resistivity of the thermal interface material is at least IO12Q*m.

[0031] Compared to a thermal interface material with 100% low conductivity filler such as alumina, the thermal interface materials of the present disclosure exhibit greater overall thermal conductivity values. Compared to a thermal interface material with 100% high conductivity filler such as aluminum nitride (~20-50x the cost of calcined alumina), the thermal interface materials of the present disclosure provide excellent overall thermal conductivity and decreased material costs while maintaining desired viscosity and dispensability characteristics. Ratios of the fine constituent to the coarse constituent, and ratios of the first filler component to the second filler component within one or more of the fine constituent and the coarse constituent, are important for establishing these desired characteristics for a thermal interface material, such as an electrically insulating thermal interface material.

[0032] The thermally conductive interface material may further include one or more of a reaction inhibitor(s), dispersant(s), coupling agent(s), and rheology modifier(s). Reaction inhibitors can include substances that adjust the rate of a chemical reaction or stop the chemical reaction. In one example, the reaction inhibitor of the present disclosure can adjust cure rate of vinyl and hydride functional silicone systems that cure via hydrosilylation. Various reaction inhibitors may be utilized for the thermal interface materials of the present disclosure. In one example, the reaction inhibitor includes silicon. In one non-limiting example, the reaction inhibitor includes methylvinyl cyclic inhibitors.

[0033] Dispersants can be added to the thermal interface material or precursors thereof to improve separation of particles and / or to improve the viscosity. These dispersants can improve dispersion and / or stabilization of particles in the thermal interface material. In one example, the dispersant may include a Polydimethylsiloxane (PDMS)-soluble wetting agent. In another example, the dispersant includes titanate. Coupling agents can be added to the thermal interface material or precursors thereof to enhance / create bonds between materials. For example, coupling agents can be used as an adhesion promoter. In one example, coupling agents of the present disclosure include silane coupling agents. In another example, coupling agents of the present disclosure include vinyl trimethoxy silane (VTMO).

[0034] Rheology modifiers are additives which modify one or more physical properties of the formulation to which they are introduced. To minimize the impact on the performance of thermally conductive materials, thixotropic rheological modifiers may be used to increasethe viscosity of the dispersion at low shear rates while maintaining flowability at high shear rates. Common rheological modifiers include fumed silica and nanoclay. In one example, the rheology modifier includes fumed, high surface area metal oxide and / or fused, high surface area metal oxide. In another example, the rheology modifier includes one or more of fumed silica and sub-micron spherical metal oxide. These modifiers may be dispersed as very fine particles and can form aggregates in a controlled manner at rest state (no flow) to reduce particle settling.

[0035] Thermal interface materials of the present disclosure may be formed by mixing two or more of a curable component, cure activator component, catalyst, reaction inhibitor, dispersant, coupling agent, and rheology modifier. For example, mixing may include using a mixer under vacuum. Each of these possible components may be added and mixed in various orders, and each of these components may be added in the liquid form. In one non-limiting example, a mixture may be formed using two unique vinyl-terminated PDMS components with distinct viscosity values, such as viscosity values ranging from about 50 to about 1000 cP. The particulate filler may be added during or after this mixing process. Alternatively, the particulate filler may be present in one of the liquid components prior to mixing. For example, materials may be provided in a two-part composition, wherein the particular filler is dispersed within one of the parts. These two parts may be initially separate. Thermal interface materials of the present disclosure may be sold as a kit, wherein the kit includes at least two separate components to be mixed for curing.

[0036] FIG. 1 illustrates apparatus 100 including thermally conductive interface material 130, according to some embodiments. Apparatus may include a heat-generating apparatus and / or an electronics apparatus. Embodiments of the present disclosure include an apparatus 100, wherein the apparatus includes a heat producing component 110, a heat dissipating component 120, and a thermally conductive interface material 130. Thermally conductive interface material 130 includes thermal interface materials of the present disclosure. As shown, the thermally conductive interface material 130 is in contact with the heat producing component 110 and the heat dissipating component 120. In one example, heat producing component 110 includes an electronic component or a battery. Therefore, it is useful for thermally conductive interface material 130 to be electrically insulating. In another example, heat dissipating component 120 includes a metal heat dissipating component, optionally including one or more fins for enhanced heat dissipation. Accordingly, thermally conductiveinterface material 130 transfers heat from the heat producing component 110 to the heat dissipating component 120.

[0037] In one example, thermally conductive interface material 130 includes a material (of the present disclosure, such as a polymer matrix), and a thermally conductive and electrically insulating particulate filler dispersed in the material, wherein the particulate filler includes a first filler component and a second filler component, wherein the first filler component has a first thermal conductivity and an aspect ratio of between 0.5 - 1.5, and the second filler component has an aspect ratio of between 0.5 - 1.5 and a second thermal conductivity that is at least 50% greater than the first thermal conductivity, and wherein between 40-70 vol.% of the total particulate filler comprises a coarse constituent having a first mean particle size (dso) of between 20 and 120 pm, and between 10-25 vol.% of the total particulate filler comprises a fine constituent having a mean particle size of between 100 nm and 5 pm, the fine constituent including at least 20 vol.% of the second filler component.

[0038] Importantly, these thermal interface materials of the present disclosure may be used as liquid dispensable thermal interface gap fillers. For example, the gap filler may be used for electronic applications with gaps greater than 1.5 mm. The materials of the present disclosure may be used for narrow bondlines, where the maximum particle size determines the gap. These thermal interface materials exhibit high thermal conductivity values while maintaining desired dispensability and viscosity characteristics. Further, these thermal interface materials are lower cost compared to many conventional thermal interface materials. Importantly, since these thermal interface materials are electrically insulating, they may be used for a broad range of electronics applications.Example 1 - Thermal Interface Material

[0039] Formulations were prepared using a speed mixer under vacuum. The liquid components included a polydimethylsiloxane (PDMS) blend containing a mixture of 50 and 1000 cP vinyl-terminated PDMS and 100 cP hydride functional PDMS crosslinker, a titanate dispersant, a 2% platinum Karstedt catalyst, and a methylvinylcyclic inhibitor. The particulate filler included (1) a 53:47 blend of 40 pm spherical alumina and aluminum nitride at 44% loading by volume; (2) 10 pm spherical alumina with alkylsilane surface treatment at 19% loading by volume; (3) ~2 pm irregular surface-treated alumina and aluminum nitride with ratio varied; and sub-pm spherical alumina.

[0040] The composition is summarized in Table 1, and the thermal conductivity is shown in FIG. 2. FIG. 2 illustrates the thermal conductivity of a thermal interface material as a function of the aluminum nitride volume fraction in the fine constituent, according to some embodiments. The thermal conductivity of the formulation with 100% aluminum nitride was 6.2 W / m*K and replacing the aluminum nitride with alumina reduced the thermal conductivity to about 5.0 W / m*K, keeping total particulate filler volume fraction constant. The individual thermal conductivity of aluminum nitride and alumina is 130 and 30 W / m*K, respectively. However, the thermal conductivity significantly increased by replacing 20% - 40% of the alumina with aluminum nitride.Table 1. Composition of thermal interface material.

[0041] While the disclosure has been described with reference to an exemplary embodiment(s), it will be understood by those skilled in the art that various changes may be made, and equivalents may be substituted for elements thereof without departing from the scope of the embodiment(s). In addition, many modifications may be made to adapt a particular situation or material to the teachings of the embodiment(s) without departing from the essential scope thereof. Therefore, it is intended that the disclosure is not limited to the disclosed embodiment(s), but that the disclosure will include all embodiments falling within the scope of the appended claims. Various examples have been described. These and other examples are within the scope of the following claims.

Claims

WHAT IS CLAIMED IS:

1. A thermally conductive interface material comprising: a matrix material; and a thermally conductive and electrically insulating particulate filler dispersed in the matrix material, wherein the particulate filler includes a first filler component and a second filler component, wherein the first filler component has a first thermal conductivity and an aspect ratio of between 0.5 - 1.5, and the second filler component has an aspect ratio of between 0.5 - 1.5 and a second thermal conductivity that is at least 50% greater than the first thermal conductivity, wherein between 40-70 vol.% of the total particulate filler comprises a coarse constituent having a first mean particle size (dso) of between 20 and 120 pm, and between 10-25 vol.% of the total particulate filler comprises a fine constituent having a mean particle size (dso) of between 100 nm and 5 pm, the fine constituent including at least 20 vol.% of the second filler component.

2. The thermally conductive interface material of claim 1, wherein the matrix material includes at least one of a polymer, an oligomer, an oil, and a thermal grease.

3. The thermally conductive interface material of claim 1, wherein the material includes an organopolysiloxane.

4. The thermally conductive interface material of claim 1, wherein the fine constituent includes between 40-60 vol.% of the second filler component.

5. The thermally conductive interface material of claim 4, wherein the fine constituent includes at least 40 vol.% of the first filler component.

6. The thermally conductive interface material of claim 1, wherein the first filler component is selected from alumina, aluminum trihydrate, and zinc oxide, and the second filler component is selected from aluminum nitride and boron nitride.

7. The thermally conductive interface material of claim 1, wherein the thermal conductivity of the first filler component is at least 5 W / m*K.

8. The thermally conductive interface material of claim 1, wherein a volume ratio of the first filler component to the second filler component in the coarse constituent ranges from 70:30 to 40:60.

9. The thermally conductive interface material of claim 1, wherein between 5-30 vol.% of the total particulate filler comprises a medium constituent having a third mean particle size (dso) of between 5-20 pm.

10. The thermally conductive interface material of claim 9, wherein the particulate filler further includes an ultrafine constituent having a mean particle size (dso) that is less than the mean particle size of the fine constituent.

11. The thermally conductive interface material of claim 1, wherein the aspect ratio of the first filler component ranges from 0.8 - 1.2, and the aspect ratio of the second filler component ranges from 0.8 - 1.2.

12. A thermally conductive interface material comprising: a polymer matrix; and a thermally conductive and electrically insulating particulate filler dispersed in the polymer matrix, wherein the particulate filler includes a first filler component and a second filler component, wherein the first filler component includes alumina, and the second filler component includes aluminum nitride, wherein between 40-70 vol.% of the total particulate filler comprises a coarse constituent having a first mean particle size (dso) of between 20 and 120 pm, and between 10-25 vol.% of the total particulate filler comprises a fine constituent having a mean particle size of between 100 nm and 5 pm, the fine constituent including at least 20 vol.% of the second filler component.

13. The thermally conductive interface material of claim 12, wherein the fine constituent includes between 40-60 vol.% of the second filler component, and wherein the fine constituent includes at least 40 vol.% of the first filler component.

14. The thermally conductive interface material of claim 12, wherein the polymer matrix includes an organopolysiloxane, and wherein a volume ratio of the first filler component to the second filler component in the coarse constituent ranges from 70:30 to 40:60.

15. The thermally conductive interface material of claim 12, wherein between 5-30 vol.% of the total particulate filler comprises a medium constituent having a third mean particle size (dso) of between 5-20 pm.

16. The thermally conductive interface material of claim 15, wherein the particulate filler further includes an ultrafine constituent having a mean particle size (dso) less than the fine constituent.

17. The thermally conductive interface material of claim 12 further comprising at least one of a catalyst, a reaction inhibitor, and a dispersant, wherein the polymer matrix includes an organopolysiloxane.

18. The thermally conductive interface material of claim 12 further comprising at least one of a coupling agent and a rheology modifier, wherein the polymer matrix includes an organopolysiloxane.

19. A heat-generating apparatus, the heat-generating apparatus comprising: a heat producing component; a heat dissipating component; and a thermally conductive interface material including: a material; and a thermally conductive and electrically insulating particulate filler dispersed in the material,wherein the particulate filler includes a first filler component and a second filler component, wherein the first filler component has a first thermal conductivity and an aspect ratio of between 0.5 - 1.5, and the second filler component has an aspect ratio of between 0.5 - 1.5 and a second thermal conductivity that is at least 50% greater than the first thermal conductivity, wherein between 40-70 vol.% of the total particulate filler comprises a coarse constituent having a first mean particle size (dso) of between 20 and 120 pm, and between 10-25 vol.% of the total particulate filler comprises a fine constituent having a mean particle size of between 100 nm and 5 pm, the fine constituent including at least 20 vol.% of the second filler component.

20. The heat-generating apparatus of claim 19, wherein the heat producing component includes a battery.

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